I made a nice tutorial that demonstrates how to easily and effectively use keyframes for these smooth and visually pleasing transition effects. I rendered out the video that was created and put it in the tutorial, so that a person will see the value of the workflow technique I teach in this. Keyframing is relatively new to Shotcut, but it is a powerful effect.
Here is how you get to the video. The forum will not let me post a link, which is kind of silly Search: “Scott Davis Keyframe Scale” and it will appear in a Google search.